Systems and Methods for Closed Loop Control to Ensure a Constant Current Output with a Changing Load Resistance

1. A system comprising: a voltage source configured to generate an input voltage waveform; a variable gain voltage amplifier configured to receive the input voltage waveform from the voltage source and provide an output voltage to a load; and a feedback component, coupled to a current return of the adjustable gain amplifier, comprising a set point voltage source configured to generate a set point voltage and an amplifier configured to compare an output of a current power detector circuit to the set point voltage, wherein the feedback component is configured to determine the voltage delivered to the load by sampling current into the load over a time period, estimating a power based on the current into the load over the time period, and wherein a gain of the adjustable gain amplifier is adjusted based on a difference between the output of the current power detector and the set point voltage so the current power output to the load remains constant.

2. The system of claim 1 , wherein the power is estimated by calculating a root mean square of the current into the load.

3. The system of claim 1 , wherein the current power detector comprises a resistor in series with the load to sample the current into the load and a voltage amplifier to determine the output of the current power detector.

4. The system according to claim 1 , wherein the feedback component further comprises a second amplifier configured to receive the output and the set point voltage and provide the difference between the output of the current power detector and the set point voltage to adjust the gain of the adjustable gain amplifier.

5. The system according to claim 1 , wherein the system stimulator is configured to reduce charge accumulation at a tissue-electrode interface, wherein the load is tissue.

6. The system according to claim 1 , wherein the current power is independent of an impedance of a load when the impedance of the load changes more slowly than a rate at which the feedback component varies the gain of the adjustable gain amplifier.

7. The system according to claim 1 , wherein the voltage source provides a low output impedance and the low output impedance reduces charge accumulation at a tissue-electrode interface.